LONDON, April 23 (Reuters) - Aviva (AV.L: Quote , Profile , Research ), Britain's biggest insurer, said on Monday Patrick Snowball, the head of its UK business, is to quit the firm at the end of June.

Snowball, who joined Norwich Union in 1989 but was beaten to the top job at Aviva by Moss, will become deputy chairman of Towergate Partnership, a fast-growing UK non-life insurer.

Aviva's announcement of Snowball's departure confirms an earlier Reuters story that he was leaving, citing a source familiar with the situation.

In a wider reshuffle of top posts by incoming group Chief Executive Andrew Moss, Aviva said Simon Machell, currently chief executive of Norwich Union General Insurance, will become head of its Asia Pacific business.

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